A slide fastener comprises a pair of substantially identical stringer halves having confronting edges provided with respective rows of coupling heads so positioned and spaced that, upon movement of a slider along these rows, the heads can be interdigitated to close the fastener or can be separated to open it depending upon the direction of movement of the slider. The of a respective coupling coil made of a synthetic-resin monofilament also having shanks reaching toward the interior of a respective support tape. Each turn of each coil is formed with, in addition to a coupling head, a coupling member or part that connects it to the adjacent turn and that is somehow connected to the textile tape to hold the coil in place on the edge thereof.
While tapes of different constructions are widely used and there are many different ways of connecting the coupling coil to the tape, the present invention is concerned with woven tapes in which the coupling coil is woven into the tape and is fed like another warp filament to the latter as the tape is formed in an automatic tape-weaving machine in a direction parallel to the warp so that the coupling coil is engaged by the weft in the weaving process. Such a process is described in detail in U.S. patents 2,651,330 and 3,545,497 of Mostertz and Burbank, respectively, in German patent document 2,359,434 of C. Menegatto, and in the book Bandwebtechnik (Verlag Sauerlander; 1988) by Hans Walter Kipp. In such arrangements the warp comprises at its outer edge a pair of so-called wing warps that in effect give the warp the section of recumbent Y with a pair of arms that vertically flank the coupling member. The warp wings are alternately shedded and aligned with the needle of a shuttleless loom that makes with each back-and-forth a double pick, in conjunction with a hook on the opposite side of the shed, so that the coupling parts of the coil turns lie between the warp wings and the weft filaments wrap around them.
The problem with this system is that the coupling element is a fairly hard-to-handle and bulky coil compared to the warp. As it bends and moves with the process it becomes very difficult to maintain and exact pitch or longitudinal spacing between adjacent coupling heads. Similarly once installed the weft filaments that secure it laterally to the tape have a poor purchase on the angled coupling parts, so that there is little to ensure that, even if set correctly at manufacture, exact pitch is maintained. Such pitch must, however, be very exact in the slide-fastener stringer halves in order to ensure that the fastener they eventually form will close readily and thereafter remain closed. Too close spacing makes the fastener very difficult to close and difficult to open, and too wide spacing makes the fastener open when not intended.
Frequently as described in German patent document 3,612,612 and in the above-cited Burbank patent the coil is provided with a filler cord that is constituted as a thick multistrand filament that extends up within the helicoid formed by the coupling coil. Such a cord gives a good purchase to the weft filaments and in general stabilizes the coupling member. In such an arrangement there is little shifting of the turns of the coil once the stringer tapes are assembled, but the coil shifts on the tape prior to being woven into the tape and such misplacement is then preserved when the weft is installed. In addition, the weft filaments, when looped around the filler cord, typically constrict it and thereby effectively shorten the cord. The coupling coil which surrounds the filler cord is not correspondingly shortened, so that this shifting of the cord in the coil can cause periodic displacements and dislocations that are reflected in undesired pitch irregularities.
The point at which the coil is fed to the weaving location is relatively distant from this location and the warp-yarn holder of the automatic weaving machine which feeds the warp yarns to this location is generally located between the coil feeder and the weaving location. The coil runs practically without tension through the feeder and to the weaving location.